1. Field of the Invention
The present invention relates to an improved depth stop, removably attachable to a rotary cutting tool and particularly to a boring tool with an enlarged cutting head.
2. Description of the Related Art
Depth stops facilitate precision drilling by regulating the depth to which a drilling tool penetrates a work piece to an operator-selected distance. A typical depth stop includes a body that slips over a drilling tool and is removably attachable to the drilling tool, for example, by a set screw extending through the body. The stop is secured to the drilling tool at a selected position which defines the depth to which the drilling tool can penetrate a work piece. Once the stop comes into contact with the work piece, the tool can penetrate no further into the work piece. Because the stop is typically fixed to the drilling tool so that it can not rotate with respect thereto, the stop continues to rotate with the tool when it comes into contact with the work piece, thus marring the surface of the work piece. Marring is minimized if the portion of the stop that comes into contact with the work piece is rotatable with respect to the body of the depth stop so that when that portion comes into contact with the work piece, it stops rotating as the body and drilling tool continue to rotate.
Depth stops for drilling tools having rotatable contact structures are known in the art. Drilling tools such as drill bits, however, typically have a constant diameter along their length, at least for the portion of the drilling tool at which a depth stop would be attached. Certain boring tools, such as, for example, Forstner bits or multi-tip spur bits, have a substantially different structure as compared with conventional drill bits. Such bits may have an elongated, constant diameter shank portion, one end of which is inserted into and held by the chuck of a drilling machine. A cutting head located at the opposite end of the shank is a generally cylindrical structure of constant diameter, typically larger than the diameter of the shank. The cutting head may have radially and circumferentially extending cutting blades at its free end. The cutting head is also typically relatively short in axial length, and, therefore, attaching a depth stop thereto can be problematic.
Proficiency of the depth stop can be impaired by the presence of drilling debris around the hole being cut by the rotary cutting tool. Such debris can prevent the depth stop from contacting the surface of the work piece being cut, thus causing the depth of the hole regulated by the depth stop to be inaccurate. U.S. Pat. No. 3,000,239 proposes a depth stop structure comprising two diametrically opposed axially extending legs, the bottom ends of which contact the work piece to arrest advancement of the cutting tool into the work piece. Although debris may escape from between the legs, the device proposed in the '239 patent is merely sandwiched between an annular shoulder of the cutting tool and the chuck of the drilling machine; the device cannot be selectively fixed at a desired axial position along the cutting tool. Moreover, with only two diametrically opposed legs, the device is inherently unstable in the lateral direction.
In addition, fixing the non-rotating portion of the depth stop to the cutting tool by means of set screws extending radially into a body of the depth stop presents certain disadvantages. Installing, adjusting, and removing the depth stop is cumbersome and time consuming because of the need to tighten and loosen the set screw or set screws. Moreover, the set screw itself requires an additional tool, such as a screw driver or allen wrench. Also, a set screw tightened against a cutting tool can mar the tool itself, especially if the depth stop turns with respect to the cutting tool while the set screw is tightened against the tool. If the set screw is tightened against the cutting blades of a drill bit, the resulting marring of the blades by the set screw can impair performance of the drill bit.